Program f11dbfe
! F11DBF Example Program Text
! Mark 28.4 Release. NAG Copyright 2022.
! .. Use Statements ..
Use nag_library, Only: f11daf, f11dbf, nag_wp
! .. Implicit None Statement ..
Implicit None
! .. Parameters ..
Integer, Parameter :: nin = 5, nout = 6
! .. Local Scalars ..
Real (Kind=nag_wp) :: dtol
Integer :: i, ifail, la, lfill, liwork, n, nnz, &
nnzc, npivm
Character (1) :: check, milu, pstrat, trans
! .. Local Arrays ..
Real (Kind=nag_wp), Allocatable :: a(:), x(:), y(:)
Integer, Allocatable :: icol(:), idiag(:), ipivp(:), &
ipivq(:), irow(:), istr(:), iwork(:)
! .. Executable Statements ..
Write (nout,*) 'F11DBF Example Program Results'
Write (nout,*)
! Skip heading in data file
Read (nin,*)
! Read order of matrix and number of nonzero entries
Read (nin,*) n
Read (nin,*) nnz
la = 2*nnz
liwork = 7*n + 2
Allocate (a(la),x(n),y(n),icol(la),idiag(n),ipivp(n),ipivq(n),irow(la), &
istr(n+1),iwork(liwork))
! Read the matrix A
Do i = 1, nnz
Read (nin,*) a(i), irow(i), icol(i)
End Do
! Read the vector y
Read (nin,*) y(1:n)
! Calculate LU factorization
lfill = -1
dtol = 0.E0_nag_wp
pstrat = 'C'
milu = 'N'
! ifail: behaviour on error exit
! =0 for hard exit, =1 for quiet-soft, =-1 for noisy-soft
ifail = 0
Call f11daf(n,nnz,a,la,irow,icol,lfill,dtol,pstrat,milu,ipivp,ipivq, &
istr,idiag,nnzc,npivm,iwork,liwork,ifail)
! Check value of npivm
If (npivm>0) Then
Write (nout,*) 'Factorization is not complete'
Else
! Solve P L D U x = y
trans = 'N'
check = 'C'
ifail = 0
Call f11dbf(trans,n,a,la,irow,icol,ipivp,ipivq,istr,idiag,check,y,x, &
ifail)
! Output results
Write (nout,*) ' Solution of linear system'
Write (nout,'(E16.4)') x(1:n)
End If
End Program f11dbfe